Optimal Irrigation for Onion and Celery Production and Spinach Seed Germination in Histosols

Increasing water scarcity in humid regions requires that food production increase its water use efficiency. Because the hydraulic characteristics of Histosols are different from those of mineral soils, water management for vegetable production must be adapted accordingly. The objective of this research was to determine the optimal soil water potential for irrigating onion (Allium cepa L.), celery (Apium graveolens L.), and spinach (Spinacia oleracea L.) crops in muck soils. Onion and celery were subjected to three irrigation treatments scheduled when tensiometer readings reached –10 or –20 kPa for onion and –30 or –50 kPa (2008) and –15 or –30 kPa (2009) for celery compared with drier control treatments for both crops. For spinach, two irrigation treatments (–10 and –20 kPa) and a control (drier) were tested. Optimal onion marketable yields and jumbo size were obtained from irrigation at potentials above –20 kPa at the bulbing stage. Celery had the best yields with the treatments of 2009 relative to the drier control. The highest spinach germination rate and yield were obtained at –10 kPa. Reliable estimates of the optimal thresholds were consistent with calculations performed using a simple analytical solution to Richards’ equation and soil characteristics. Irrigation thresholds for matric potential in a muck soil were shown to be crop specific and could be derived from a model and basic soil hydraulic characteristics.